Maintaining consistent and uniform tones is a desired goal in image forming apparatus and devices. For example, it can be desirable for an image to appear the same no matter which rendering system renders the image and no matter how many times an image is rendered on a particular system. The image should exhibit, for example, the same lightness or hue each time it is rendered on a given system and no matter on which system it is rendered. For this reason, rendering engines, such as print engines in a printing system, are put through a color verification (or color validation process) in order to evaluate whether the print engines realize appropriate color reproducibility.
In the color verification process, a plurality of color measurement pages, each of the plurality of color measurement pages having a plurality of color patches, are printed and measured by a measuring device, for example, a color sensing device in the image forming apparatus, and then each color measured by the measuring device is compared with a corresponding target color.
If one of the measured colors does not match the corresponding target color, color corrections can then be made to the image forming apparatus during a color calibration process.
As for a high-end printer in which high color reproducibility is required, thousands of color patches can be printed in one color verification process, and the verification process can be repeated with a short interval.
In addition, in a print shop, for example, Kinko's®, the print shop would perform the color verification process on each of the color printers or MFPs, for example, first thing in the morning (for example, before the shop opens) to ensure the color accuracy of each of the color printers or MFPs. Usually, the print shop will print and measure a set of color charts from a printer or a MFP with an inline scanner and spectrophotometer. For example, a set of color charts can contain multiple pages of color chart, for example, 50 or more pages.
In some situations, the color printer or MFP may experience an interruption, for example, a paper jam, during or after the color verification process. After the paper jam is cleared, the verification process or procedure needs to be restarted, which results in the color printer or MFP having to re-print an entirety of the color charts from the beginning, for example, each and every page of the color chart, starting with page 1, since printer conditions can change after an interruption in the printing process. Especially, in a case of jam, color conditions are likely to change. For example, after the paper jam is cleared, the entire verification process has to be restarted when a paper jam occurs, no matter how many pages were printed before the jam occurred. The restarting of the verification process can result in lost time and use of additional materials. For example, during the printing of a set of color charts, for example, a 50 page color chart, and a paper jam occurs at page 49, then all pages printed before the jam occur are wasted, and the previously printed 49 pages need to be reprinted and measured again.